"This never happened."
As Keine turned again to leave, her power kicked in. Cirno, Reimu, and Marisa had forgotten completely about Keine and Shin having been there, and were dazed and confused for a few minutes. After the disorientation, there was really only one question left on their minds.
"Why are the spellcard duel walls up?"
--
Cirno fell down, exhausted from the fight she had had with Marisa and Reimu. The miko and witch had initially teamed up against Cirno, who had actively tried to freeze as many bullets as she could, but one stray charm Reimu had shot had accidentally hit Marisa, who was charging up a Master Spark. This turned the two friendly rivals against each other, with the ice fairy taking advantage of the situation. At the end of it all, all three parties realized what they had been doing and laughed off the tension, enjoying the little bit of time they had spent together.
Cirno, in particular, had more than a little fun. Sure, her brain was configured like most fairies, in which she usually thought of pranks not unlike how humans think of breakfast: it's something that happens in the morning, it's fun, and there's no real consequence most of the time. However, after having been beaten by both Reimu and Marisa twice, Cirno wanted to see why everyone else seemed to gravitate to them. Besides pranks and eating iceberries, there really wasn't much that she could do; any time she had spent with any Daiyousei would be practically erased after either's faux extermination, and a fairy spending time with a human would seem like a prank to anyone else, keeping her fairly safe and free. It was flawless!
And as long as she stayed friendly with the two 'figures', then she'd be definitely alright.
"Let's do this again, Marisa, Reimu. And next time I'll be the strongest too!"
=Cirno Happy End=
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All side characters have a happy/okay/bad end, but most of the time their actual end has no further implication on the story. There are exceptions (like Cirno) however.